Swiveling screw propeller



Aug. 14, 1945.

w. A. LOTH ETAL SWIVELLING SCREW PROPELLER Filed NOV. 1939 9Sheets-Sheet l lNi/ENTORS WILLIAM ARTHUR LOTHAND SEBASTIENNE MARIE.HENRIETTE-GUYOT 3v M,%Q'Z:ATTORNE)G Aug. 14, 1945. w QT|-| ETAL2,382,431

SWIVELLING SCREW PROPELLER Filed Nov. 7, 1939 9 Sheets-Sheet 2 IAMRTHUFJQVESJFB I??? WILL- A 4 SEBASTIENNE MARIE HENRIETTE GUVOTA"TTORNE.Y5

Aug. 14, 1945. w. A. LQTH ETAL 2,382,431

SWIVELLING SCREW PROPELLER Filed Nov. 7, 1939 9 Sheets-Sheet 3 UR LOTHAND NRIETTE. GUYOT M 8 ATTOR N 5Y5 .INVENTORS: ARTH ARIE HE WILLIAMSEBASTIENNE M Aug. 14, 1945. w. A. LOTH ET AL 2,382,431

SWIVELLING SCREW PROPELLER Filed Nov. 7. 1939 9 Shee-ts- Sh'eet 4INVENTORS WILLIAM ARTHUR LOTH SEBASTIENNE. MARIE HENRIETTE GUYOT Aug.14, 1945. w. A. LOTH ETAL 2,382,431

SWIVELLING SCREW PROPELLER Filed Nov. 7, 1939 9 Sheets-Sheet 5 WWW ATTORN 5Y5 Aug. 14, 1945. w. A. LOTH ETAL 2,382,431

SWIVELLING SCREW PROPELLER Filed Nov. 7, 1939 9 Sheets-Sheet 6 INVENTORSWILLIAM ARTHUR LOTH AND SEBASTIENNE MARIE HENRI ETTE GUYOT ATTORNEYSAug. 14, 1945. w. A. LO'LI'H ET A].

7 2,382,431 SWIVELLING SCREW PROPELLER Filed Nov. 7, 1959 9 Sheets-Sheet7 FIGTZ v A \um' A "7'"" INVENTORS: WILLIAM ARTHUR LOTH AND SEBASTIENNEMARIE HENRIETTE GUYOT RNEYS -Aug. 14, 1945. w. A. LOTH ETAL SWIVELLINGSCREW PROPELLER Fild NW. '7. 1939 9 Sheets-Sheet 8 w or a MTZ 6U AW 5 NH M v. TTNE E NMANE -N E N R MHFLH O A E T U V T L WMB A FIG. 9

Aug. 14, 1945.

W. A. LOTH ETAL SWIVELLING SCREW PROPELLER Filed NOV. 7, 1939 9Sheets-Sheet 9 INVENTORSI WILLIAM ARTHUR 5 LOTH AND SEBASTIENNE MARIEHENRIETTE GUYOT Maxie/ 4 ATTRNE/YS Patented Aug. 14, 1945 SWIVELIN GSCREW PBOPELLER William Arthur Loth and Sebastlenne Marie HenrietteGuyot, Paris, France; vested in the Allen Property Custodian ApplicationNovember 7,1939, Serial No. 303,182 In France July 81, 1936 6 Claims.(Cl. 170-164) This patent application is a continuation in part of ourearlier patent application Serial No.

156,064 filed on July 28, 1937, now Patent No. 2,241,786 granted May 13,1941, for Stabilisation of aircraft and in particular of aircraft basedon lifting systems which are mobile relatively to them or on systemswhich are at the same time lifting and propelling and mobile relativelyto them," and certain parts of the present application will be found inthe earlier application.

The present invention relates to screw propellers the hub of which ismounted on a driving shaft bymeans of a universal joint so that the axisof rotation of the propeller can be freely displaced into any angularposition relatively to said shaft within an imaginary cone the apex ofwhich coincides with the centre of the joint, the axis of the conenormally coinciding with the axis of rotation of the propeller. Thisproperty which the propeller possesses is hereinafter referred to asswiveling.

Certain portions of the apparatus herein are also shown in our mentionedPatent No. 2,241,786, such as the stator and rotor and their mutualspherical bearings, connections and general arrangement, the inventionbeing based on certain improvements in said structure and particularlyof the means for producing the inclination of the axis of the rotor withrespect to that of the stator.

According to the present invention a swiveling screw propeller asdefined above is characterised in that the said joint has its partsrotating in synchronism in that it maintains the ratio of theinstantaneous speeds of rotation of the propeller and of thedrivingshaft constant for all angular positions of the axis of rotationof the propeller within the cone, and also during the entire duration ofall movements of inclination of the axis of rotation of the propellerrelatively to the driving shaft.

This property of having the parts of the joint rotating synchronously isnot displayed by Cardan joints in which the ratio of the instantaneousspeeds of inclined driving and driven shafts is constant only at certainpoints during rotation.

A further characteristic feature of the invention resides in the factthat when the propeller is in' clined so that the axis of rotationthereof coincides with the surface of the imaginary cone the apex angleof which has been preselected according to the conditions, the propelleris subjected to an impulse (hereinafter referred to as a precessionimpulse) which compels the axis of rotation of the propeller to describea portion of said conic surface (the precession cone). In this thepropeller relative to the driving axis either manner the axis ofrotation of the propeller reaches a position in which the propellerexerts a stabilising torque as will be explained hereinafter. Thisprecession impulse takes place without producing (and consequentlyhaving to overcome) acceleration and deceleration forces, owing to thefact that the joint is of the synchronously rotating class.

The operation previously described is not affected by adjustment of theaxis of rotation of before or during movement of the body which thepropelleris propelling-in, the case of an aeroplane during flight forinstance.

It is to be understood that a swiveling screw propeller in accordancewith the present invention is not to be limited as to the type ofmovable body with which it may be associated. This may be an aeroplane,land vehicle, surface water vessel or under water craft and this broadapplication is to be understood when the term movable body" is usedthroughout the description and claims.

Joints of-the synchronously rotating class are well knownper se andthere is a type of such joint which comprises spherical membersdrivingly coupled to each other by a series of balls engaging meridianrace grooves in the adjacent faces of said members, and a cage engagingsaid balls which are maintained in a diametral plane.

We are aware that it ha previously been proposed in BritishSpecification numbered 878 of 1903, to mount a swiveling screw propelleron an airship by means of a joint which is adapted to maintain constantthe ratio of the instantaneous speeds of rotation of the propeller andof the driving shaft when the axis of rotation of the propeller has beendisplaced to a new position but which forces the propeller to undergocertain variation in the speed of rotation while it is being displacedwith respect to the driving shaft. Such a joint therefore does notfulfil the condition of synchronous rotation as defined above.

It'has previously been proposed in the gimbal mountings of apparatusused on board ships, aircraft or other oscillating bodies or in similaruniversal joint mechanisms to provide two gimbal rings, universal jointsor the like arranged in series between the apparatus and the oscillatingbody, the two rings or joints being connected by a Cardan membercontrolled by the relative inclination of the apparatus and theoscillating body so that a constant-velocity (homokinetic) coupling isprovided therebetween.

The accompanying drawings illustrate, by way of example only, someembodiments of the invention.

Figure 1 is a sectional elevation of a propeller hub constructed inaccordance with the present invention;

Figure 2 is on a smaller scale; the same being a sectional plan viewtaken on the line IIbIIb of Figure 1; Figure 2A is a sectional plan viewtaken on the line IIa-IIa of Figure 1;

Figure 3 is a sectional elevation of a second construction;

Figure 4 is an elevation of a helicopter provided with the propellershown in Figure 3;

Figures 5, 6 and '7 are diagrammatic views showing the operation of thehomokinetic joint and mechanism for bringing the propeller into thestabilising position in which the stabilising torque is then exerted;

Figure 8 is a sectional elevation of a constructional embodimentcorresponding to Figure 3;

Figure 9 is a partial horizontal section made according to line IIc-IIcof Figure 8.

The most general problem of the control of a swiveling propeller asapplied by way of example to helicopters will now be described atlength, stress being laid on the problem of stabilisation.

. Referring to Figures 1 and 2 of the accompanying drawings; the rotorblades P are secured to one element of the synchronously rotating jointgenerally indicated by Y the element bein adapted to be rotated (whennot inclined) about the vertical axis Am which in the non-inclinedcondition coincides with the axis V of the drivin shaft. On the lattershaft (which is not shown) is mounted pinion I which drives the joint Ythrough reduction gear J and the ring gear K.

The mechanism described above is enclosed within a casing Cy which isformed in two separate parts, the upper part F and the lower part F1which may be considered to be parts of the fuselage or stator.

A bearing R4 is disposed between the casing Cy and the joint Y to enablethe rotor to be rotatably driven around the casing, whilst a thrustbearing'Ra is also provided between the joint and casing.

The synchronously rotating joint comprises the two elements having thespherical surfaces S1 and Se.

A groove T1 is formed on the surface S1 and a second groove T2 is formedon the surface Se, both said grooves being equally inclined but inopposite directions to a meridian passing through a ball B. The groovesare adapted to cooperate and have maintained therebetween the ball B.There are provided three pairs of such grooves spaced equally around thejoint each pair with a ball (see Figure 2), which balls are associatedwith a connecting cage E extending around said joint. Any device may beused which maintains the centres of the balls in a plane bisecting theangle between the axes of the driving and driven shaft when the latteris inclined with reference to the former.

It should be noted that if the grooves are perfect loxodromics (that isare parts of curves which cross all the meridians of the spheres at thesame angle of inclination) it follows that the balls will be maintainedon a diametrical circle as with this arrangement the balls areautomatically maintained in the bisecting plane.

From the above description it is clear that the synchronously rotatingjoint Y is rotatably driven from the pinion I, through reducing gear J,ring gear K, and due to the coaction of the balls B and grooves T1 andT2 the drive is transmitted to the outer element of the joint and henceto the blades P. It will also be apparent that it is possible todisplace the outer spherical element relative to the inner element(thereby inclining the plane of the-rotor blades) and it is clear thatsince the joint is homokinetic this may be done without varying thespeed of rotation of the rotor.

A stabilising mechanism is provided in conjunction with thesynchronously rotating joint mounting of the blades P.

This mechanism comprises a driving annulus C1 disposed between bearingsR1 and R2 (respectively engaging the upper part F5 of the casing Cy andthe inner element of the joint Y) said annulus being driven by the innerelement through a ring gear U1 (secured to said element) and reductionplanet gears S engaging a ring gear U2 secured to said annulus C1.

A driven annulus C2 which is capable of engagement with the drivingannulus C1 is mounted within the outer element of joint Y by means of abearing Ra so that it is free to rotate therein. The outer face of theannulus C1 or the inner face of annulus C2 is faced with any well knownfriction lining material. The two faces (of the annuli C1 and C2) are sodesigned that upon the outer spherical element of the homokinetic jointbeing inclined the faces are gradually brought into engagement untilthey ultimately become wedged and locked together.

There will firstly be described how, when the rotor is subjected todisturbance, it is in consequence subjected by the stabilising mechanismto an artificial precession movement, and, secondly, the effect of thelatter.

The stabilising mechanism becomes operative when the rotor is subjectedto a disturbance so that the axis of the rotor is moved into an inclinedposition with reference to the axis of the driving shaft to such anextent that the rotor axis coincides with the surface of theprecessioncone which we will assume has an apex angle of twice Referringto Figure 6, let it be assumed that a squall strikes the helicopter inthe direction indicated by arrow D, so that the rotor is movedrelatively to the stator from the position indicated in full lines to aposition in which the righthand blade is below the full line position(shown in chain-dotted lines W).

Due to the fact that the rotor is inclined by the squall the axis ofrotation of the rotor will be moved from the vertical Am towards A0 (seealso Figures 5 and '7) Whilst inclination of the rotor axis towards A0is taking place the rotor due to its rotation will act as a gyroscopethe axis of rotation of which is inclined to the vertical. As a resultof the gyroscopic effect produced the rotor axis will be rotated aroundvertical axis V. When the axis of the rotor becomes inclined at angle ato the vertical (which takes place at some point A), annulus C2 will bebrought into engagement with annulus G1 which will by a rolling actiontherefore drive annulus C2 and the latter will freely rotate in theouter spherical element. When due to the squall the axis of rotation isinclined at angle q) to the vertical (so that the axis coincides withthe surface of the precession cone) which is assumed to take place atpoint A1 (Figures 5 and 7) locking engagernent between the annuli C2 andC1 takes place at point 0 (Figure 7). This locking engagevertical.

ment is such that annulus C: can no longer freely rotate in the outerspherical element but is con-s strained to move round with point ethereof in contact with annulus C1 as the latter rotates, carrying withit the outer spherical element in an artificial precession movement.Consequently the axis of the annulus C2 (which is also the axis ofrotation of the rotor) is compelled to describe a portion of the surfaceof the precession cone between the points A1 and A2 (Figures 5 and 7).It is seen therefore that the annulus and rotor have been subjected toan artificial precession movement and swiveled around by annulus Cluntil the axis of rotation of the rotor and annulus C: reaches A2. Atthis point the th'rust B (see Figure 6) of the rotor produces'astabilising torque the value of which is S; (a: being the perpendiculardistance of the line of action 01' the thrust from the centre of gravityK of the helicopter).

This stabilising torque counterbalances the squall and nullifies theeffect thereof. In Figure 6 it is indicated by the arrow D1, and theposition of the rotor after it has been swiveled and during the actionof the thrust in the direction of axis S is shown in the dotted positionZ.

It is assumed that the squall is persistent and exerted in the samedirection, that is from A: towards As (Figure 5) so that when the rotorhas been swiveled into the dotted position Z the squall will tend tomove the rotor back towards the horizontal position. This results indisengagement of annulus C: from the locked position with annulus G1 at0, so that annulus C2 is again driven by annulus C1 in free rotation inthe outer spherical element. This tendency for the squall to move therotor towards the horizontal position is opposed by the stabilisingthrust itself so that a balanced state is set up.

As the squall dies away, the rotor returns to the initial horizontalposition, and its axis Am once again becomes vertical and coincides withV.

Considering the effect of the synchronously rotating joint during thesequence of events described above it is assumed that in Figure 5, m isthe diagrammatic representation of a rotor blade when the axis ofrotation of the rotor is When due to the squall the rotor is inclinedwith reference to the vertical axis and assuming it has reached theposition A1 (that is the axis of rotation of the rotor is on the conicsurface of the precession cone) then blade 10 will take up position 1'1.When the rotor is being made to swivel by the precession mechanism fromA1 to A2 and the axis of rotation of the rotor has pased through angle1' and reached the position A1, in view of the fact that the joint ishomokinetic the position of the blade n at position As will be m whichwith respect to an imaginary planepassing through Am, A3 lags by anangle 1 assuming of course that the rotor is not being rotatably driven.

The synchronously rotating joint therefore has the effect of eliminatingduring swiveling of the rotor any tendency for the rotor blades toadvance or retard as is the case with a Cardan joint. With the latterthe blade is advanced or retarded during swiveling of the rotor andproduces acceleration or deceleration forces which would.

have to be overcome by the precession mechanism.

If the rotary motion of the driving shaft is resumed, in any swivelingmovement of the rotor the blades will strictly retain their own drivenrotation (that is they will not be accelerated or retarded).Consequently the energy required to produce rotation of the rotor whenchanging from Point A: to A: will be neither increased nor decreased.This enables easy starting and maintenance of a swiveling movementwithout the necessity for additional expenditure of energy in overcomingsuch forces of acceleration and retardation.

In Figure 3 there is shown a constructionin which the rotor may beadjusted to an initial inclination with reference to the driving shaft.Thus if it is desired to incline the rotor so that a forward drivingcomponent is produced this may be effected in the construction shownwithout causing locking engagement of the annuli Cz and C1 andconsequent swiveling of the rotor. Should the rotor be inclined fromthis initial position of adjustment due to a disturbance (such as asquall striking the machine) so that the axis of rotation reaches thesurface of the cone of precession (the geometric axis of which is theaxis of rotation of the rotor in its initially adjusted position) therotor will be compelled to describe a portion of said conical surface.

In Figure 3 (as described with reference to Figure 1) the rotor blades Pare secured to the joint Y which rotates on bearing R4.

The precession mechanism comprises a carrier member C3 disposed betweenbearings R1 and R2 (respectively engaging the upper part Fa of thecasing and the inner spherical element of the joint), said carriermember being driven from the joint through a ring gear U1 (secured tothe inner spherical element of the joint) and reduction planet gears Sengaging a ring gear U2 secured to said member Ca.

In the mechanism shown in Figure 3 the driving annulus Ciis not in fixedrelationship to the inner spherical element but is capable of sliding onthe carrier member C3. In order that the annulus C1 may be rotatablydriven by member C3 their adjacent faces are provided with a pluralityof elongated grooves C4 and C5 respectively. These grooves are regularldisposed around the annulus and carrier member and have balls Cs mountedtherebetween. The latter form the common driving element.

A driven annulus G2 which is capable of engagement with the drivingannulus C1 is mounted on the outer spherical element of the joint Y bymeans of the bearing R3 so as to be free to rotate therein.

Suitable means (not shown) are provided for sliding the annulus C1 oncarrier member C3, whilst the rotor is being tilted to bring its axisinto the initially inclined position above referred to. Annulus C1 isslid on member C3 so as to be inclined to the driving axis by the sameamount as the rotor and annulus C2. This means that the annuli C1 and C2are maintained parallel during and after tilting thereof.

This initially inclined axis of rotation of annulus C1 and of the rotornow constitutes the geometric axis of the cone of precession.

When the axis of rotation of the rotor is inclined to said geometricaxis (as by a squall) to such an extent that it reaches the surface ofthe cone of precession, annulus C2 engages lockingly with annulus C1 andthe mechanism producing artificial precession is brought into operationas before.

The propeller blades may be provided with means for varying the pitch ofthe blades without departing from the scope of the invention.

Figures 8 and 9 show a constructional embodiletters and numeralsdesignate the same parts as in Figure 3.

In Figures 8 and 9 are shown:

At N, the transmission of the driving movement to the shaft of thereducing device,

At 01, a bushing which can be taken to pieces and which allows themounting of balls B,

At 0;, the three pin joints which allow the moun ing of the cage for theballs B,

At i set screws which allow of determining the orientation of theartificial precession mechanism.

In this constructional embodiment use is made of a means for incliningthe rotor from the exhaust gases of the engine. This means is only anexample among others to which recourse may be had.

Said embodiment comprises the following:

An exhaust ring H1 secured to the stator, having a connection X to theexhaust of the engine (not shown), a collector-for the gas H2 secured tothe hub of the rotor and consequently rotat- 25 ing with the latter.Segments H3 are included which can be adjusted by a rod X1, for example.so as to allow the admission of the gases of the exhaust ring Hi to thecollector H2 through the apertures H4 and H5 when the segment H3 3 isshifted by rod X1 to form an opening H6.

In Figure 8, the segments are assumed to be closed at the left and openat the right of said figure. It results therefrom, in this case, fromthe fact that the exhaust gases are projected 35 from the open segmentsof ring Hi to the collector H2, that these gases definitely tend toproduce an inclination of the rotor to the left, which would result, infact, in a rearward inclination, 4o

owing to the gyroscopic effect.

In this embodiment, it is necessary to distinguish:

(1) The mechanism controlling the inclination of the rotor obtained inthis case by a differential azimuthal emission of the gases into therotor;

(2) The mechanism controlling the orientation of the stabilising system,shown in the drawings,

by screws (connected to the pilot) adjusting the position of the annulusC1.

Of course, after having determined by means of the first mechanism theinclination of the axis of the rotor, the pilot sets, parallel to saidaxis, the axis controlling the stabilization, by r .1

means of the second mechanism.

What we claim as our invention and desire to secure by Letters Patentis:

l. A swiveling screw propeller having a support and a drive shaft, a hubdriven from said drive shaft, propelling and sustaining blades mountedon said hub, a universal joint associated with said hub connecting theblades with said drive shaft and having means associated therewith tocause the driven and driving portions of said joint to rotate uniformlysynchronously in all angular positions of the axis of the propeller withrespect to the drive shaft and during movements of inclination of theaxis of r0- tation of said propeller with respect to said drive shaft inorder to attain new relative angular positions, and fluid operatedprecession means for stabilizing the axis of the propeller, includinggas ejecting means on the support receiving exhaust gases from theengine driving the propeller and a gas collector mounted on the hub,together capable of imparting a precession impulse to said propeller soas to cause the axis of rotation thereof to trace a portion ofthesurface of the hub whenever the axis of said propeller tends to departfrom the axis of said hub and attains the surface thereof.

2. A swiveling screw propeller according to.

claim 1, having means for adjusting the axis of rotation of thepropeller to an initial position at 0 an angle to the drive shaft andallowing said propeller to swivel in said initial position.

3. A swiveling screw propeller having a support and a drive shaft, a hubdriven from said drive shaft, propelling and sustaining blades mountedon said hub, a universal joint associated with said hub connecting theblades with said drive shaft and having means associated therewith tocause the driven and driving portions of said joint to rotate uniformlysynchro- 0 nously in all angular positions of the axis of the propellerwith respect to the drive shaft and during movements of inclination ofthe axis of retation of said propeller with respect to said drive shaftin order to attain new relative angular positions, the universal joint,the means associated therewith as well as the hub including an innerspherical element rotating about the fixed axis of the drive shaft andsecured to said shaft, an outer spherical element directly carrying theblades and rotating about the displaceable axis of rotation of thepropeller, a plurality of ball bearings distributed about the innerspherical element, pairs of intersecting grooves formed in the outersurface of said inner spherical element and in the inner surface of saidouter spherical element, said grooves being inclined to the axis of saidspherical elements, and a cage surrounding said inner spherical memberand formed with opening means confining said balls in a diametricalplane and in the corresponding pairs of grooves.

4. A swiveling screw propeller having a support and a drive shaft, a hubdriven from said drive shaft, propelling and sustaining blades mountedon said hub, a universal joint associated with said hub connecting theblades with said drive shaft and having means associated therewith tocause the driven and driving portions of said joint to rotate uniformlysynchronously in all angular positions of the axis of the propeller withrespect to the drive shaft and during movements of inclination of theaxis of rotation of said propeller with respect to said drive shaft inorder to attain new relative angular positions, precession means capableof imparting a precession impulse to the propeller so as to cause theaxis of rotation thereof to trace a portion of the surface of the hubwhenever the axis of said propeller tends to depart from the axis ofsaid hub and attains the surface thereof, said precession meansincluding a stabilizing mechanism comprising an inner spherical element,a first annular friction member, means mounting said first annularfriction member to turn with said inner spherical element while beingfree to assume inclinations with respect to said inner sphericalelement, an outer spherical element surrounding said inner sphericalelement and carrying a second annular friction member which is freelyrotatable relative to said outer spherical element, and means arrangedto cause the first annular friction member and the second annularfriction member to be brought into frictional engagement with each otherwhen the axis of rotation of the propeller becomes in clined to apredetermined extent with respect to the axis of the drive shaft, sothat the first annular friction member will impart a swiveling movementto said second annular friction member and tothe outer sphericalelement, whereby said propeller receives an imparted processions-lmovement bringing said propeller into a position in which the thrustthereof exerts a stabilizing torque, and adjusting means on said supportfor selectively predetermining the angular position of said firstannular friction member on said inner spherical element so as todetermine the orientation of said precession means.

5. A swiveling screw propeller having a support and a drive shaft, a hubdriven from said drive shaft, propelling and sustaining blades mountedon said hub, a universal joint associated with said hub connecting theblades with said drive shaft and having means associated therewith tocause the driven and driving portions of said joint as rotateuniformly-synchronously in all angular positions of the axis of thepropeller with respect to the drive shaft and during movements ofinclination of the axis of rotation of said propeller with respect tosaid drive shaft in order to attain new relative angular positions, theuniversal joint, the means associated therewith as well as the hubincluding an inner spherical element rotating about the fixed axis ofthe drive shaft and secured to said shaft, an outer spherical elementdirectly carrying the blades and rotating about the displaceable axis ofrotation of the, propeller, a plurality of ball bearings distributedabout the inner spherical element, pairs of intersecting grooves formedin the outer surface of said inner spherical element and in the innersurface of said outer spherical element, said grooves being inclined tothe axis of said spherical elements, and a cage surrounding said innerspherical member and formed with opening means confining said balls in adiametrical plane and in the corresponding pairs of grooves, said cagecomprising a ring and said opening means comprising holes through thering substantially conformably receiving the balls, said ring beingmovably positioned in a space formed between the inner and outerspherical elements permitting said ring limited movementcircumferentially and vertically with respect to said inner and outerspherical elements as the balls move in the intersecting grooves as theinner and outer spherical elements are moved relative to each other.

6. A swiveling screw propeller having a support and an engine drivendrive shaft, a hub driven from said drive shaft. propelling andsustaining blades mounted on said hub, a universal joint associated withsaid hub connecting the blades with said drive shaft and having meansassociated therewith to cause the driven and driving portions of saidjoint to rotate uniformly synchronously in all angular positions of theaxis of the propeller with respect to the drive shaft and duringmovements of inclination of the axis of rotation of said propeller withrespect to said drive shaft in order to attain new relative angularpositions, and fluid operated precession means for stabilizing the axisof the propeller, including gas ejecting means on the support receivingexhaust gases-from the engine driving the propeller and a gas collectormounted on the hub, together capable of imparting a precession impulseto said propeller so as to cause the axis of rotation thereof to trace aportion of the surface of the hub whenever the axis of said propellertends to depart from the axis of said hub and attains the surfacethereof, said gas collector having apertured segments thereon againstwhich the elected gas impinges, said segments being adjustable to modifythe reception of ejected gas by the collector in a manner to control therotor deflecting eflect of the ejected Bases.

